This invention relates to a novel polysilane and to a method of forming a pattern for semiconductor devices by means of lithography using an organosilicon polymer such as polysilane.
In the manufacture of a semiconductor device, various steps are performed, such as the processing of a silicon-based insulation film, e.g., a silicon oxide film, a silicon nitride film a silicon oxynitride film for a spin-on-glass. The processing of these silicon-based insulating film is usually performed as follows.
Namely, a resist film is formed on an insulating film at first and then this resist film is subjected to exposure and development, thereby forming a resist film pattern. This resist film pattern is then employed as an etching mask in the following dry etching process, thus making it possible to process the insulation film. In order to ensure a desired resolution and exposure dose margin or focus margin in the exposure step, the thickness of the resist is required to be made thinner. However, if the thickness of the resist is too thin, the resist pattern may be completely etched away during the dry etching process of the insulating film, thus making it impossible to continue the processing of the insulating film. In order to solve this problem, a method has been developed wherein an etching mask and a resist are formed on an insulating film, and the resist pattern is transferred onto the etching mask, and then dry etching of the insulating film is performed.
In this case, the following materials have been employed as a material for such an etching mask, i.e., (a) silicon-based materials such as polysilicon and amorphous silicon; (b) carbon; and (c) resin materials such as novolak resin and polyhydroxystyrene.
However, these materials for an etching mask are accompanied with the problems to be explained below with reference to FIGS. 1 and 2. FIGS. 1 and 2 illustrate a state wherein an etching mask 3 and a resist 4 are deposited and patterned on a silicon-based insulating film 2 formed on a silicon substrate 1.
When the etching mask material of (a) is employed, the reflection light from the etching mask in the exposure step becomes too strong, so that a standing wave may be generated in the resist, whereby making the side wall of the resist pattern corrugated in shape as shown in FIG. 1.
On the other hand, the etching mask materials of (b) and (c) are capable of functioning as an anti-reflective coating, so that the aforementioned problem may be overcome. However, since these etching mask materials exhibit a small etch rate ratio in relative to the resist, the resist pattern may be disappeared during the etching of these etching masks. In particular, in the case of etching mask consisting of carbon, the profile of the pattern to be obtained may become tapered as shown in FIG. 2.
Furthermore, since the etching mask materials of (a) and (b) are formed into a film by means of a CVD method or a sputtering method, the process becomes complicated and leads to an increase in manufacturing cost as compared with the process where a film is formed by means of coating. On the other hand, if the material of (c) is employed in combination with a silicone-containing resist, it is possible to achieve a sufficiently large etch rate ratio between the resist and the etching mask. However, there is a problem that the silicone-containing resist is relatively low in resolution and in exposure dose margin or focus margin as compared with the ordinary resists.
As explained above, it has been impossible according to the prior art to obtain an etching mask material which can be formed into a film by means of coating, which is capable of suppressing the reflecting light in the exposure step, which exhibits a large etch rate ratio in relative to a resist, and which is excellent in dry etching resistance. Under the circumstances, an organosilicon polymer such as polysilane is now considered as a promising etching mask material which is capable of overcoming the aforementioned problems. However, if an organosilicon polymer is to be employed as an etching mask, features such as mechanical strength and heat resistance are of course required for the polymer. Further, if a resist solution is to be coated on an etching mask comprising an organosilicon polymer thereby to form a resist film, some measures are required to be taken so as to prevent a mixing between an etching mask and a resist.
Furthermore, when a resist is processed through exposure and development steps to form a resist pattern, and then an etching mask is to be etched by means of reactive ion etching (RIE) with the resist pattern being employed as a mask, the etching mask may be accumulated with electric charges (charge-up), which may lead to a dielectric breakdown of an insulating film in the worst case. For the purpose of realizing an increasingly refined processing, a specific method can be taken wherein a resist is once exposed to ultraviolet rays (and developed if required), and then unexposed portions are further exposed to electron beam (EB exposure) and subjected to development thereby to obtain a very fine pattern. In this EB exposure, if the resist is suffered from the charge-up, the electron beam may be repulsed by the electric charges and hence drifted. In this case, since regions other than the regions to which the exposure is intended to be directed may also be exposed to the electron beam, it is no more possible to perform a desired fine processing. Therefore, it is desired to overcome the problems involved due to the charge-up in the processing step employing an etching mask and charged particles such as an electron beam.